1. The Field of the Invention
The present invention relates to systems and methods for separating condensable vapors (e.g., carbon dioxide) from gases by desublimating the condensable vapors in a heat exchange liquid.
2. The Related Technology
The separation of carbon dioxide from other light gases such as nitrogen is important for achieving carbon dioxide sequestration. Flue gas from a conventional power station typically includes from about 4% (vol.) to about 16% (vol.) carbon dioxide (CO2). It is commonly believed that this CO2 represents a significant factor in increasing the greenhouse effect and global warming. Therefore, there is a clear need for efficient methods of capturing CO2 from flue gases so as to produce a concentrated stream of CO2 that can readily be transported to a safe storage site or to a further application. CO2 has been captured from gas streams by several technologies, the most common of which include: oxyfiring, where oxygen is separated from air prior to combustion, producing a substantially pure CO2 effluent; absorption, where CO2 is selectively absorbed into liquid solvents; membranes, where CO2 is separated by semi-permeable plastics or ceramic membranes; adsorption, where CO2 is separated by adsorption on the surfaces of specially designed solid particles; chemical looping, where carbon oxidation and oxygen consumption are physically separated by a recycled intermediate, typically metal oxide; and low temperature/high pressure processes, where the separation is achieved by condensing the CO2.
In the past, the most economical technique to capture CO2 from a flue gas has been to scrub the flue gas with an amine solution to absorb the CO2. This technology has been used commercially for small-scale processes and for specialty processes. However, it has not been adopted in utility-scale power plants, primary because the technology causes an unacceptable decrease in the total efficiency of the power plant.
Another type of process that has received significant attention is the oxy-combustion systems, which uses oxygen, usually produced in an air separation unit (ASU), instead of air, for the combustion of the primary fuel. The oxygen is often mixed with an inert gas, such as recirculated flue gas, to keep the combustion temperature at a suitable level. Oxy-combustion processes produce flue gas having CO2, water and O2 as its main constituents; the CO2 concentration being typically greater than about 70% by volume. Treatment of the flue gas is often needed to remove air pollutants and non-condensed gases (such as nitrogen) from the flue gas before the CO2 is sent to storage.